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The M31 NEWFIRM Survey


NEWFIRM Survey of Intermediate Age Populations in M31's Halo: A Test of ΛCDM

Owing to their long dynamical times, galaxy stellar halos provide unique insight into their formation history. Recent detailed hydrodynamical and N-body simulations, carried out within the framework of a ΛCDM cosmogony, can track the formation of single Milky Way sized galaxies. It is clear from these simulations that halo stars can have three distinct origins: accretion of satellites, in situ formation, and kicked up disk. Studies of these populations in the Milky Way are complicated by our internal perspective, but the Andromeda galaxy (M31) offers the ideal combination of an external global perspective and detail. The SPLASH (Spectroscopic and Photometric Landscape of Andromeda’s Stellar Halo) team used KPNO/4-m+MOSAIC optical (M, T2, DDO51) imaging of 72 fields and Keck/DEIMOS spectroscopy of a few ×104 RGB stars across this area to discover the true metal-poor halo of M31 and has measured key properties out to 2/3 of the virial radius (R ~200 kpc): surface brightness profile, substructure, kinematics, [Fe/H], and [α/Fe]. By adding to this the KPNO/4-m+NEWFIRM wide-field near-infrared (J, KS) imaging survey of intermediate-age AGB stars, it is possible to obtain the critical missing piece for testing halo formation models: a constraint on the stellar age distribution in M31’s halo.

M31 NEWFIRM Survey at a Glance

PI(s) Puragra Guhathakurta and Rachael L. Beaton
Proposal ID 2012B-0540
Years of Observation 2012-2014
Targets M31 satellites and tidal features over a field centered on M31
Field −9° < α < 27°, +27° < δ < +54°(J2000)
Bands JX, KXS
Median Seeing 1.1 arcsec
Number of stacks 137 (JX), 158 (KXS)